Intervertebral disc defects can be treated by removal of the defective intervertebral disc by surgery and osseous fusion of the intervertebral space with the two adjacent vertebral bodies. In this method the sections of the vertebral column adjacent to the fused vertebral column segment can be overstressed, especially in the area of the intervertebral disc. Another method for treatment is to remove the defective intervertebral disc and, thereafter, to insert an artificial intervertebral disc. In the majority of cases, the rear facet joints and the ligamentous apparatus also are damaged severely. Thus, there is usually no longer any natural control of movement of the artificial intervertebral disc from the posterior side. Consequently, high shearing and rotational forces have an abrasive effect on the vertebral column segment being treated.
DE 42 39 715 C2 describes a fixation system for stabilizing vertebrae, in which rotational and alternating pressure and tension loads on the part fixed in the bone can be reduced. However, elastic damping or control of the occurring movements is not possible.
EP 0 669 109 B1 describes a device for stabilizing adjacent thoracic vertebrae allowing a damaged intervertebral disc and the intervertebral joints to be partially released from stress from the posterior side. The device comprises two pedicle screws which are rigidly connected, respectively, to a strap consisting of an elastic synthetic material and which are connected to one another via the biased strap. A pressure-resistant body slipped onto the elastic strap is further provided between the two screw heads to transmit pressure forces. The use of a textile strap of this kind with a pressure-resistant body, however, does not enable any multi-axial guidance stability of the motion segment of a vertebral column.
U.S. Pat. No. 5,474,555 describes a polyaxial bone screw with a screw element and a receiving part connected thereto for receiving a rod which allows limited motion between the receiving part and the vertebra. However, elastic damping of the motion is not possible with this screw.
U.S. Pat. No. 5,961,356 describes an anchoring element in form of a polyaxial bone screw which has a pressure element acting upon the head, wherein the pressure element comprises a spring element acting upon the inserted rod.
U.S. Pat. No. 5,562,737 discloses an extra-discal intervertebral prosthesis comprising at least a partially closed, elongated body including a compression chamber having an elastic block at one end. The block has a free face abutted by a ball joint associated with a first of two fixation means engageable in spaced vertebrae of a patient.
Thus, new anchoring devices continue to be sought which allow dynamic anchoring of a mechanical device, such as, e.g. a rod, in a bone or a vertebra and which can be used in particular for a dynamic stabilization device for stabilizing motion control and relieving the stress on an artificial intervertebral disc. In addition, it is desirable to have a dynamic stabilization device for bones, in particular for vertebrae, which allows motion control and stress relief on the human intervertebral disc from the posterior side.